Selective sublimation/desublimation separation of ZrF4 and HfF4

Abstract

The separation of zirconium and hafnium, which is essential in the nuclear industry, is difficult due to the great similarities in their chemical and physical properties. In contrast to the traditional aqueous chloride separation systems, the current process focuses on dry fluoride-based technologies, which produce much lower volumes of chemical waste. In the present work, separation is achieved in both a sublimation and a desublimation step, where the Zr/Hf mole ratio varies between 160 and 245 across the length of desublimer and 86 to 40 within the sublimer. Model predictions for the sublimation/desublimation rates fit the experimental results well, with deviations becoming more apparent as sublimation proceeds. This may be attributed to crust formation preventing the system from reaching thermodynamic equilibrium. The model adequately predicts time- and temperature-dependent mole ratios of both the sublimer residue and of the desublimed mass.